1. Field of the Invention
The present invention relates to a permanent magnet synchronous rotating electric machine and a rotor core.
2. Discussion of the Background
Recently, from viewpoints of prevention of global warming and resource conservation, duties to be performed by a vehicle such as a hybrid car, and an industrial power saving machine are becoming very important. In order to perform the duties, it is necessary to reduce CO2-discharge, and improve the amount of energy consumption and efficiency.
For such the vehicle such as the hybrid car or the industrial power saving machine, a permanent magnet type synchronous rotating electric machine is required, which has characteristics that high output and high-speed rotation are possible, reliability is high and efficiency is good, rotation speed is variable, and controllability is good. As a rotating electric machine satisfying this condition, there is a synchronous motor in which a permanent magnet is included in a rotor, that is, an interior permanent magnet (IPM) motor. Since this motor providing size reduction and weight reduction are realized, the range of its use in the field of the industrial power saving machine is increasing. For example, the motor is applied also to a crane, a winding machine, an elevator, an elevator of a multi-level parking zone, a compressor or a blower for wind or water power, a fluid machine such as a pump, and a processing machine including mainly a semiconductor manufacturing member or a machine tool. In the present embodiment, IPM motor will be mainly described
FIG. 6 is a front view of an electromagnetic steel plate forming member blanked to mold a rotor core in a first related art.
In FIG. 6, an electromagnetic steel plate forming member 35 is composed of a thin disc-shaped electromagnetic steel plate for forming a rotor core. In this electromagnetic steel plate forming member 35, a magnetic hole 31 for inserting therein a permanent magnet is provided per pole when the rotor is formed. An outer bridge 32 is formed between this magnet hole 31 and a circumferential surface of the rotor. When the plural electromagnetic steel plate forming member 35 are laminated in the block shape, an electromagnetic steel plate laminator (rotor core 34 in FIG. 7) is manufactured (refer to, for example, JP-A-2006-211826, Specification P.4, and FIGS. 1 to 3 and Toyo Denki Technical Report No. 111, 2005-3, P.13 to P.21).
Next, the operational principle of the interior permanent magnet motor will be described.
FIG. 7 is a front sectional view of a main part of an interior permanent magnet motor to which the rotor in the first related art is applied. In the shown motor, the number of magnetic poles of permanent magnets of the rotor is six poles, and the number of magnetic poles of salient poles of a stator (the same number as the number of slots) is 36 pieces.
In FIG. 7, regarding the operation of the motor, in the rotor 30 in which a permanent magnet 33 is inserted into the interior of a rotor core 34, the gap flux density becomes high in a q-axis constituting a magnetic convex portion which is small in magnetic resistance, and the gap flux density becomes low in a d-axis constituting a magnetic concave portion which is large in magnetic resistance. By such the saliency of the rotor 30, the following relation is produced: Lq>Ld, when Lq is q-axis inductance and Ld is d-axis inductance. Therefore, reluctance torque produced by change in flux density in addition to magnet torque may be used, so that more increase in efficiency may be expected. The magnet torque generates by a magnetic attraction force and a magnetic repulsion force between a magnetic field by the permanent magnet 33 of the rotor 30 and a rotating magnetic field by a stator winding housed (not-shown) in a slot 42 in a stator core 41 of the stator 40. The reluctance torque generates by attraction of the salient pole portion of the rotor 30 to the rotating magnetic field by the stator winding (not shown).
Next, a second related art will be described with reference to FIG. 8.
FIG. 8 is a front view of an electromagnetic steel plate forming member blanked to mold a rotor core in the second related art (refer to, for example,    JP-A-2005-039963, Specification P.4 to P.6, and FIGS. 1 and 2,    JP-A-2005-057958, Specification P.4 to P.7, and FIGS. 1 and 5,    JP-A-2005-130604, Specification P.8, and FIG. 1,    JP-A-2005-160133, Specification P.8, and FIG. 1,    JP-A-2002-112513, Specification P.5, and FIGS. 1 and 3, and    JP-A-2006-254629, Specification P.7 and P.8, and FIG. 4.)
In FIG. 8, an electromagnetic steel plate forming member 50 is composed of a thin disc-shaped electromagnetic steel plate for forming a rotor core. In this electromagnetic steel plate forming member 50, two magnet holes 52 and 53 are provided in the V-shape so that two magnets per pole are inserted on the rotor outer diameter side symmetrically with respect to radial pole pitch lines provided at a predetermined pole pitch angle, when a rotor is formed. An outer bridge 54 is formed between the outer end portion of the magnet holes 52, 53 and a circumferential surface of the rotor. Further, in the electromagnetic steel plate forming member 50, a center bridge 51 is provided between the magnet holes 52 and 53. When the plural electromagnetic steel plate forming member 50 are laminated in the block shape, an electromagnetic steel plate laminator (rotor core 57 in FIG. 9) is manufactured.
Next, the operation will be described with reference to FIG. 9.
FIG. 9 is a front sectional view of a main part of an IPM motor to which the rotor in the second related art is applied, which shows schematically a positional relation of poles between a stator and a rotor which generate optimum rotating torque. FIG. 10A and 10B are diagrams for explaining of the operation of the IPM motor in the second related art. FIG. 10A is a schematic diagram showing the operation when the motor rotates normally, and FIG. 10B is a diagram showing a relation between a current phase which generates a rotating magnetic field of the motor and torques. The number of magnetic poles of permanent magnets of the rotor in the shown motor is eight poles, and the number of magnetic poles of salient poles of a stator (the same number as the number of slots) is 48 pieces.
In FIGS. 9 and 10A, the IPM motor has a permanent magnet type rotor 50 in which permanent magnets 55, 56 having the same size as the size of magnet holes 52, 53 are inserted into the magnet holes. In such the constitution, a magnetic field by the permanent magnets 55, 56 embedded in the interior of a rotor core 57 and a rotating magnetic field by a stator winding housed (not-shown) in a slot 62 in a stator core 61 of a stator 60 attract and repel each other, thereby to generate a magnet torque. Further, since the magnetic resistance in the direction of a q-axis orthogonal to the direction of a d-axis which is a magnet axis becomes smaller than that in the d-axis direction, saliency structure is provided. Therefore, a q-axis inductance Lq becomes larger than a d-axis inductance Ld, and reluctance torque generates by this saliency. In FIGS. 9 and 10A, the permanent magnets 55, 56 which are embedded in the magnet holes 52, 53 and arranged in the V-shape are isosceles. Therefore, a repulsion-boundary point of magnetic fluxes by the permanent magnets in an outer iron core portion sandwiched between the two permanent magnets having the same size which are opposed to each other in the same poles is located in the center of the outer iron core portion of the rotor 50, and on a center line OC passing through a center of the radial pole pitch lines OP.
In FIGS. 9 and 10A, though a force for giving rotary energy to the rotor 50 is actually composed by strength of current flowing in the stator winding (not shown) in the slot 62 and the like, its description is simplified here. Flux density distribution of the motor will be described, paying attention to a pole located at 12 o'clock.
The d-axis repulsion-boundary point of the outer iron core portion surrounded by the two permanent magnets 55, 56 of the same polarity is located in the center of the surface of the rotor 50. In case that the poles formed by the stator windings (not shown) in the slots 62 are shown as in FIGS. 9 and 10A, on the gap surface between the stator 60 and the rotor 50, the left side with respect to the repulsion-boundary point on the line OC becomes an attraction part constructed so that the stator is the N-pole and the rotor is the S-pole, and the right side with respect to the repulsion-boundary point on the line OC becomes a repulsion part constructed so that both of the stator and the rotor become the S-pole. On the surface of the rotor 50, the attraction part becomes dense in magnetic flux and the repulsion part becomes sparse in magnetic flux. Therefore, magnet torque which is about to move the rotor 50 from the side in which the magnetic flux is dense to the side in which the magnetic flux is sparse, that is, in the clockwise direction acts on the rotor 50. Further, the q-axis flux flows mainly in teeth 63 of the stator 60 opposed to the salient poles.
In the description related to FIG. 10A, since attraction is produced between the magnetic fields by the permanent magnets 55, 56 of the rotor 50 and the rotating magnetic fields by the stator windings (not shown) in the slots 62 and the d-axis salient pole portion of the rotor 50 is attracted to the rotating magnetic field by the stator winding (not shown), the flux density in the oblique line portion becomes particularly high. At this time, with respect to the S-pole component of the permanent magnets and the S-pole component by the stator windings (not shown), the N-pole component by the windings is short. Therefore, the reluctance torque which is about to move the rotor 50 in a direction where the magnetic flux of the S-pole component is shortened, that is, in the clockwise direction acts on the rotor 50.
Here, as shown in FIG. 10B, the magnet torque which is produced by the magnetic attraction force and the magnetic repulsion force between the magnetic field by the magnet and the rotating magnetic field by the winding shows a relation of a curve in the figure, and the reluctance torque generated by the attraction of the salient pole portion of the rotor to the rotating magnetic field by the winding shows a relation of a curve in the figure. Hereby, by putting the magnet torque and the reluctance torque together, a torque shown by a thick solid line in the figure may be generated.
However, in the second related art, in the outer iron core portion formed between the upper surface of the two permanent magnet insertion holes and the outer diameter of the rotor core, the q-axis flux by armature reaction is easy to be saturated. Therefore, the reluctance torque may not be utilized, so that it is difficult to obtain large torque in the starting time or in abrupt change in load.
Further, as shown in the second related art, in the shape in which the two permanent magnets are arranged in the V-shape per pole, magnetic anisotropy is stronger than that in the shape having flat arrangement of the permanent magnets as shown in the first related art. However, the anisotropy is not sufficiently used, and this shape in the second related art does not attribute to improvement of motor efficiency in the low-speed operation time and in the light-load operation time.